There are many fields of manufacture in which the interior of a base body, such as a pipe or tube, or a segment thereof, is metalized over an ordinary metal such as steel with an expensive surface layer treatment or coating that is fused to the base metal in order to provide a finished, or partly finished, part or product that will respond to manufacturing specifications, but which is less expensive than making the entire body of the same material that the specifications require. Thus, parts such as the interior of pipes or tubes used to convey corrosive or abrasive fluids, liquids, slurries and the like, are frequently required to provide thereon an interior, or concaved, metalized surface of chromium, or chrome, or other special metal or metal alloy, that will either resist corrosion and wear or will provide a good bearing surface. In strings of pipe used in deep oil wells, for example, it is desirable that the interior surface of the pipe have resistance to corrosion or wear, so as to extend the time period that a string of pipe functions before corrosion or abrasive failure causes disruption of oil production and consequent increase of costs. Similarly, strings of pipe which are used to transport concrete slurry from a source of supply to the site of use, must have a wear resistant inner surface in order to withstand the abrasion of the inner surface which is caused by the aggregate (sand, gravel, and crushed stone) which is mixed with the cement in the concrete slurry.
It has been long known that ordinary steels, except for leaded steels or resulphurized steels, may be chrome surfaced by plating or the like, to meet the specifications for desired strength of the part and provide the surface character specially required for exposure to a harsh environment in which the part is to be used.
However, chromium, for example, is a relatively expensive material, and chromium's use in various chemical baths by which chrome plating may be effected, is environmentally undesirable, operationally difficult and expensive to control. Also, it is technically difficult to deposit a metalizing layer of any substantial thickness onto the interior surface of tubes or pipes, or segments thereof, that are to serve as the bearing surface of a bearing or journal element.
While metalizing the exterior surface of bars and rods avoids, to substantial extent, the undesirable environmental effects associated with chemical plating of such bodies, the mechanical metalizing techniques previously employed in metalizing such bars and rods have usually used an open flame torch that burns fuel gases, such as acetylene, propane, or the like in the presence of oxygen, to both preheat the body surface to an elevated temperature and to heat the surface application material, which is initially in powder form, to a temperature at which the powder material will become at least partially molten and fuse onto the base material of the body. These prior art metalizing techniques have not been wholly successful for economically metalizing the exterior of tubes, since the heat of a torch will frequently burn through the wall of the tube. It will be understood that such prior art metalizing techniques also generally are not successful in metalizing the interior of elongated tubes and pipes, since access to the interior of such elongated bodies with an open flame torch is very difficult, if at all possible.
The problems with said prior technique for metalizing exterior surfaces are that there is both lack of accurate control of the thickness of the layer of the surface application material to the underlying body, and resultant lack of uniformity of the thickness of the layer that is applied by open torch heat. Furthermore, the minimum thickness of the layer of applied material usually obtained by metalizing with an open flame torch working with powdered metal, is about 0.008 inches, and the maximum thickness of a layer of applied metal is about 0.015 inches, both of which thickness values are frequently much greater than the thickness of the applied material layer which is required to be supplied to meet the performance specifications for the metalized part, and this substantially increases the cost of manufacture.
A further problem is that when using fine particles of metalizing materials to form a fused surface on an underlying body, the torch heat intensity is frequently so great that it vaporizes or burns away a substantial quantity of the finest particles of the metalizing material, thereby resulting in loss of material and economic waste. Still another problem is that, in the event a thick layer of metalizing is required to be deposited, there is insufficient control over the thickness of metal being deposited and, therefore, maintaining of concentricity of the inner surface of a metalized sleeve or journal is difficult, and machining or other expensive finishing operations must be resorted to in order to obtain a high degree of concentricity of the innermost surface of an arcuate part that has been metalized.
Other techniques are also available for metalizing with a vapor, either in an inert atmosphere or under vacuum. Such processes include chemical vapor deposition and physical vapor deposition, as by evaporation, ion plating, and sputtering. The products of these processes are coatings and free-standing shapes such as sheet, foil and tubing of thicknesses ranging from 20 nm to 25 mm. However, these processes do not lend themselves readily to the metalizing of the bore surface of long lengths of pipe or tubing.
An improved method of metalizing the interior of metal bodies is disclosed in U.S. Pat. No. 4,490,411, which discloses an apparatus and method for metalizing the interior of pipes or tubes using powdered metal. The base metal pipe or tube which is to be internally metalized is moved axially while simultaneously being rotated at a relatively high rpm. A first preheat means, preferably comprising an induction heater, heats a portion of the pipe and its interior to a first elevated temperature, and the particles of the metalizing powder are deposited into the interior of the pipe to be heated to the first elevated temperature. The rotation of the pipe distributes the fluidized particles into laminae which under further influence of centrifugal forces, automatically distributes the semi-fluidized particles effectively. The fluidized metalizing material is bonded together and to the body substrate by application of a second induction heat at a higher temperature at which the bonding then occurs between the laminae of the metalizing material and between the metalizing material and the base material of the tube or pipe. Preferably the process is performed in the presence of a non-oxidizing gas such as preheated nitrogen.
Two means are disclosed for delivering the metalizing powder to the interior of the pipe to be metalized. In one embodiment, the metalizing powder is conveyed to the interior of the pipe by means of a cantilevered boom or supply-support tube through which the metalizing powder, entrained in a stream which includes a pressurized non-oxidizing gas, is delivered in the form of a spray or shower from a nozzle in the interior of the pipe at a station located laterally or axially between the two electrical induction heating coil means, namely a first such induction heating means being a preheater and the second induction heating means being the metalizing heater for accomplishing the metal fusion. In the second embodiment, an elongated auger tube and concentric auger are utilized for delivering metalizing powder to the desired point of discharge between the first induction coil and the second induction coil.
Although the method and apparatus embodiments of U.S. Pat. No. 4,490,411 are capable of producing internally metalized pipe of acceptable quality, the disadvantage with utilizing either of the devices disclosed is that both devices must be supported interiorly of the base tubing or pipe in order to convey the metalizing powder within the center region of the pipe. This means that the process is limited to tubing or piping having a relatively large diameter. In addition, because the delivery point for the metalizing powder is within the tubing from a cantilevered boom, the apparatus is very sensitive to vibration, thereby causing the powder to be unevenly distributed throughout the inside surface of the pipe during periods of bad vibration so that thin spots and high spots of the metalizing thickness may exist upon the inside surface of the fused metalized pipe. A further disadvantage is that by the process of this patent, only short lengths of tubing can be metalized because of the problems entailed in suspending the internal boom which is delivering the metalizing powder.
With this then being the state of the art, it is one object of the present invention to provide an improved method for metalizing the interior surface of metal pipes and tubes.
It is another object of the present invention to provide an improved method of creating a novel and improved product, and the improved product itself, wherein the product is a sleeve or segment of a sleeve consisting of a tube or pipe of a base metal with an interior annulus of expensive metal or metal alloy fused to the inside of the original base tube or pipe.
It is a further object of this invention to provide an internally metalized tube or pipe wherein the thickness of the metalizing layer may be made to almost any desired dimension and may be accurately controlled so as to provide an innermost surface of very precise and concentric nature.
Another object of this invention is to provide an improved method and apparatus for metalizing the interior surface of hollow or tubular bodies with a metal in a manner that eliminates burn-up or burn-away loss of the metalizing material.
A further object of this invention is to provide an apparatus and method for metalizing the interior surface of base metal tubular bodies with relatively expensive metalizing alloys or materials, such as chrome powder, in a manner to provide an accurate control of the thickness of the metalizing layer applied, while simultaneously avoiding economic loss of the metalizing metal through undesired vaporization or burning away of the metalizing material.
Still another object of this invention is to provide a new and inexpensive method of forming a very long pipe or tubing having an internal coating of a corrosion resistant metal.
And still a further object of this invention is to use the effects of both tangential drag imparted by the inner surface of the rotating tube or pipe, and centrifugal force, upon metalizing material that has been changed by heat into at least semi-molten form to achieve a metalized surface that is laminated onto the interior of a base tubular body, and that is characterized by one or more of the following advantageous features: surprisingly and unusual uniformity of the inner surface concentricity of the layer deposited despite substantial thickness of the deposited layer; unusual hardness of the deposited metalizing layer; excellent bond between the metalizing layer and the base tubular body or substrate; and improved concentricity of the innermost surface of the metalizing layer as compared with the interior periphery of the base tube onto which the metalizing layer is deposited.
These and other objects of the present invention, as well as the advantages thereof, will become more clear to those skilled in the art from the disclosure which follows.